A project is proposed to continue the study on the structure and function relationships of streptokinase in its activity of human plasminogen activation. In previous studies, chemical modifications have been applied to free streptokinase and its complex with plasmin. These results have identified functional groups on the surface of streptokinase molecule and those possibly involved in the plasminogen binding. A second study utilized the expression of cloned streptokinase gene. Posttranslational proteolysis removed C-terminal 32 residues of streptokinase resulted in a protein with retained activity of plasminogen activation. Three new areas of investigation are proposed for the future studies. (1) Current results on chemical modifications of streptokinase will be confirmed by a 'label selection' chemical modification procedure and these approaches will be expanded to the light chain of human plasmin. (2) The properties of genetically altered streptokinase will be studied. This will be accomplished by site-directed mutagenesis and structural alterations of cloned streptokinase gene. This will be followed by the biosynthesis of structurally altered streptokinase which will be studied for its activities as plasminogen activator. (3) Fused proteins between 'kringle' structures and streptokinase will be constructed by genetic manipulations. These proteins will be tested to determine whether they have an enhanced specificity for fibrinolysis.